Photosynthesis
Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight energy to convert water and carbon dioxide into glucose and oxygen. This process is essential for life on Earth, providing the energy and organic compounds necessary for most living organisms.
Process
Photosynthesis occurs in two main stages:
1. Light-Dependent Reactions (Light Reactions):
Photosystems I and II: These protein complexes capture light energy using pigments like chlorophyll.
Electron Transport Chain: The captured light energy is used to excite electrons, which are then passed along an electron transport chain. This process generates ATP (adenosine triphosphate), an energy-carrying molecule.
Water Splitting: Water molecules are split, releasing oxygen as a byproduct and providing electrons to replace those lost in Photosystem II.
NADPH Production: The excited electrons from Photosystem I are used to reduce NADP+ (nicotinamide adenine dinucleotide phosphate) into NADPH, another energy carrier.
2. Light-Independent Reactions (Calvin Cycle):
Carbon Fixation: Carbon dioxide from the atmosphere is fixed into organic molecules using the energy from ATP and NADPH generated in the light reactions.
Sugar Formation: The fixed carbon is used to build glucose, a simple sugar that can be used for energy or stored as starch.
Cellular Respiration
Cellular respiration is the process by which cells break down glucose and other organic molecules to release energy in the form of ATP. This process occurs in both aerobic (with oxygen) and anaerobic (without oxygen) environments.
Process
Aerobic Cellular Respiration:
1. Glycolysis: Glucose is broken down into pyruvate, producing a small amount of ATP.
2. Pyruvate Oxidation: Pyruvate is converted into acetyl-CoA, releasing carbon dioxide.
3. Citric Acid Cycle (Krebs Cycle): Acetyl-CoA enters the citric acid cycle, further breaking down carbon bonds and releasing carbon dioxide and energy carriers like NADH and FADH2.
4. Oxidative Phosphorylation: NADH and FADH2 donate electrons to an electron transport chain, generating a proton gradient across the mitochondrial membrane. This gradient is used by ATP synthase to produce large amounts of ATP.
Anaerobic Cellular Respiration (Fermentation):
Glycolysis: Glucose is broken down into pyruvate, producing a small amount of ATP.
Fermentation Pathways: In the absence of oxygen, pyruvate is converted into lactate or ethanol, regenerating NAD+ for glycolysis to continue.
Interconnections
Photosynthesis and cellular respiration are interconnected processes:
Energy Flow: Photosynthesis captures solar energy and stores it in glucose, while cellular respiration releases this energy for cellular work.
Carbon Cycle: Photosynthesis removes carbon dioxide from the atmosphere, while cellular respiration releases it back.
Oxygen Cycle: Photosynthesis produces oxygen, which is essential for aerobic cellular respiration.
Significance
These processes are fundamental to life on Earth, providing energy, building blocks for organic molecules, and maintaining the balance of gases in the atmosphere.
Additional Notes
